This invention relates to a camera system for the processing of documents, in particular for reflectance and/or transmittance measurement of documents.
Such a camera system can be used for example for evaluating documents, e.g. bank notes. In usual bank note processing devices, an illumination device having a light source and a mirror assembly is used to illuminate the document to be judged, and the light reflected by the document is directed onto a detector, for example a CCD sensor, to obtain digital images of the document. The image signals can then be evaluated for various purposes.
Such camera systems are generally formed for reflectance or transmittance measurement of documents, in particular bank notes. For the light reflected by the bank note to be detected as faithfully as possible, an optic is located in the prior art between the object plane traversed by the bank note and the detector for transferring an image of the illuminated area—usually a strip—of the bank note onto the detector in reduced size. A disadvantage of known camera systems and the optics used therein is the great distance between object and detector. Furthermore, the reduction in size leads to distortions in the image generated by the optic on the detector, which require correction for useful image signals to be obtained. The usually employed light sources, for example fluorescent lamps, have only a relatively short life and must thus be replaced at certain time intervals.